Bevel gradient dichroic film for liquid crystal on silicon display and method for testing the same

ABSTRACT

A bevel gradient dichroic film for an off-axis liquid crystal on silicon display device is provided. The bevel gradient dichroic film includes a dichroic film, the dichroic film having a film characteristic, and the film characteristic of the dichroic film including a gradient direction. The gradient direction is dependent on an incident angle of an incident light so that a light spot of the incident light on the dichroic film has a light characteristic being uniformly distributed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to a display, and more particularly toa liquid crystal on silicon display, a bevel gradient dichroic film forthe same, and a method of testing the bevel gradient dichroic film,suitable for a off-axis projector system to improve the uniformity,brightness and contrast.

2. Description of the Related Art

Because the liquid crystal display (LCD) has the advantages of compactsize, lightweight, low operational voltage, low power consumption, andradiation free, it has gradually replaced the conventional CRT displayand became the main stream of the display devices. However, due to thelimitation of manufacturing technology of LCD, the size of most LCDproducts is limited to below 30 inches. Although plasma display panelcan provide a display size between 30-60 inches, most consumers cannotafford such products because of the high costs.

Hence, to provide affordable large size displays, most manufacturersadopt the projection technology such as reflective projection displaydevices and rear projection display devices. The reflective projectiondisplay device includes the liquid crystal projector (LCP), the digitallight protector (DLP), and the liquid crystal on silicon (LCOS)projection device. The rear projection display device also uses LCOStechnology. Currently, the DLP and LCOS are the most adoptedtechnologies in the market. Because the LCOS technology provides theadvantages of low cost, high aperture ratio (can be as high as 90%),high resolution (the pixel distance can be 12 um or less), more and moremanufacturers have been developing this technology.

Therefore, the LCOS projection technology is the key technology for thereflective projection display devices and the rear projection displaydevices because it can significantly reduce the cost and increase theresolution.

FIG. 1 is a schematic view illustrating a conventional LCOS projectiondevice. Referring to FIG. 1, the operation principle of the LCOS will beillustrated as follows. The light source 102 emits the white light 104and the white light 104 passes through the filter 106 and the colorseparation mirror 108 to obtain the red light 112, the green light 122,and the blue light 142. The red light 112 will reach the polarizationbeam splitter (PBS) 116 via the dichroic mirror 110 and the reflectivemirror 114.

FIGS. 2A and 2B are schematic views illustrating the operation of theconventional PBS. For example, when the red light 112 goes through thePBS 116, the PBS 116 will polarize the red light 112 and reflect onlythe S-polarized red light to the LCOS panel 118. Referring to FIG. 2A,when the video signal is to be shown on the dark panel, the S-polarizedred light will be reflected back and thus cannot enter into the X-cube152. Referring to FIG. 2B, when the video signal is to be shown on thebright panel, the S-polarized red light will be converted into aP-polarized red light 120 by the LCOS panel so that the P-polarized redlight 120 can enter into the X-cube 152.

Hence, the red light 112, the green light 122, and the blue light 142are reflected to the LCOS panels 118, 132, and 146 via the PBS 116, 130,and 144 respectively. The red light 120, green light 134, and blue light148 that are partially polarized by the LCOS panels will be combined bythe X-cube 152 to generate the video signal. Finally, the video signalwill be projected to the display via the zoom lens 154.

Hence, the color separation device (e.g., dichroic mirror) andrecombination device (e.g., X-cube) are the most important devices forthe conventional LCOS projection system. If the color separation orcolor recombination ratio between the red/green/blue light is notuniform, the uniformity and the brightness of the recombined videosignal will be seriously affected. Further, if the recombined videosignal is not in focus, the final video will be blurring and affects theresolution.

In the conventional LCOS projection system, the color separation deviceis X-cube, dichroic mirror, or dichroic filter. For example, the X-cube110 in FIG. 1 can be a color separation mirror when the direction of thepropagation of light is opposite. The dichroic mirror 110 shown in FIG.1 uses the dichroic mirror or dichroic filter. Further, the light pathand the normal direction of the reflective surface of the colorseparation device are parallel in the conventional LCOS projectionsystem, which is so-called “on-axis” design. For example, the light pathof the red light 112 is perpendicular to the reflective surface 162 ofthe PBS 116 and the reflective surface 164 of the X-cube 152.

FIG. 3A is a top view of the on-axis design of the conventional dichroicmirror. FIG. 3B is a cross-sectional view of the dichroic mirror fromthe direction of A of FIG. 3A. FIG. 3C is a cross-sectional view of thelight spot taken along the line B-B of FIG. 3A. Referring to FIG. 3B,the light 302 perpendicularly emits on the reflective surface 304 of thedichroic mirror 304. Referring to FIG. 3C, the light spot 312 of thelight 302 on the reflective surface 306 has an ellipse shape. Generally,this on-axis design can provide a light spot 312 with good coloruniformity.

When a better color uniformity is required, a dielectric or metal filmcan be coated on the dichroic mirror or filter to change thecharacteristics of the light beam propagation due to the interferenceeffect. For example, a special optical film can be coated on thedichroic mirror or filter to form a horizontal gradient coating dichroicmirror or a horizontal gradient coating dichroic filter. Hence, a moreuniform primary color lights with a higher transparent ratio can beobtained from the incident light in order to generate a betterrecombined video signal.

FIG. 4 is a schematic drawing illustrating an off-axis LCOS projectiondevice. The light source 402 emits the white light 402 and the dichroicmirror 404 separate the red light 406, the green light 408, and the bluelight 410. Those primary color lights are polarized by the polarizer 412and incident on the LCOS panel 414. The LCOS panel 414 then partiallypolarizes the red/green/blue lights. Then the analyzer 416 and thedichroic mirror 418 recombine the partially polarized red/green/bluelights to obtain the video signal. Then the video signal is projected tothe display.

A concern for the off-axis LCOS projection device is that thedistribution of the primary colors is not uniform. Even if thehorizontal gradient coating dichroic mirror or the horizontal gradientcoating dichroic filter is used in the off-axis LCOS projection device,the distribution of the primary colors is still not uniform. Therefore,how to improve the distribution of the primary colors and increase thecontrast is a very important issue.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a bevel gradientdichroic film to effectively improve the distribution uniformity,brightness, and contrast of the primary color light beams.

Another object of the present invention is to provide a LCOS projectiondevice with a bevel gradient dichroic film, in order to effectivelyimprove the distribution uniformity, brightness, and contrast of theprimary color light beams.

Still an object of the present invention is to provide a method fortesting the bevel gradient dichroic film to obtain the distributionuniformity, brightness, and contrast of the primary color light beams.

As embodied and broadly described herein, the present invention providesa bevel gradient dichroic film for an off-axis liquid crystal on silicondisplay device. The bevel gradient dichroic film includes a dichroicfilm, the dichroic film having a film characteristic, the filmcharacteristic of the dichroic film including a gradient direction.Wherein the gradient direction is dependent on an incident angle of anincident light so that a light spot of the incident light on thedichroic film has a light characteristic being uniformly distributed.

In a preferred embodiment of the present invention, the bevel gradientdichroic film includes a dielectric material or metal.

In a preferred embodiment of the present invention, the filmcharacteristic includes a dielectric characteristic or a thickness ofthe film.

In a preferred embodiment of the present invention, the lightcharacteristic of the light spot includes an energy distribution, areflective index, or a light separation ratio for different colorlights.

The present invention provides a liquid crystal on silicon displaydevice which includes: a light source for emitting a white light; acolor separation mirror for separating the white light into threeprimary color lights; a polarizer for polarizing the three primary colorlights; a liquid crystal on silicon panel for partially polarizing thethree primary color lights according to the video component of an inputvideo signal; an analyzer; and a color recombination mirror. Theanalyzer and the color recombination mirror combine the partiallypolarized three primary color lights to obtain an output video signal.Wherein a bevel gradient dichroic film is formed on at least one of thecolor separation mirror and the color recombination mirror. The gradientdichroic film includes a dichroic film, the dichroic film having a filmcharacteristic, the film characteristic of the dichroic film including agradient direction. The gradient direction is dependent on an incidentangle of an incident light so that a light spot of the incident light onthe dichroic film has a light characteristic being uniformlydistributed.

The present invention provides a method for testing a bevel gradientdichroic film. The method includes: providing an incident light having aplurality of incident angles to the bevel gradient dichroic film; andtesting a light characteristic of a dichroic light beam separated fromthe incident light at each of the incident angles to determine whetherthe light characteristic is uniform.

In a preferred embodiment of the present invention, the lightcharacteristic of the dichroic light beam includes an energydistribution, a reflective index, or a light separation ratio fordifferent color lights.

Accordingly, in the bevel gradient dichroic film and the LCOS displaydevice of the invention, the thickness gradient and characteristics ofthe dichroic film on the color separation mirror or color recombinationmirror is dependent on the angle of the incident light. Accordingly, byadjusting the direction of the thickness gradient or characteristic ofthe coating film and the distribution of the thickness or thecharacteristic of the coating film, the distribution uniformity,brightness and contrast of the primary color light beams can beeffectively improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a schematic view illustrating a conventional LCOS projectiondevice.

FIGS. 2A and 2B schematic views illustrating the operation of theconventional PBS.

FIG. 3A is a top view of the on-axis design of the conventional dichroicmirror.

FIG. 3B is a cross-sectional view of the dichroic mirror from thedirection of A of FIG. 3A.

FIG. 3C is a cross-sectional view illustrating the light spot takenalong the line B-B of FIG. 3A.

FIG. 4 is a schematic drawing illustrating an off-axis LCOS projectiondevice.

FIG. 5A is a top view of the off-axis design of the dichroic mirror.

FIG. 5B is a cross-sectional view of the dichroic mirror viewed alongthe direction of C of FIG. 5A.

FIG. 5C is a cross-sectional view illustrating the light spot takenalong the line D-D of FIG. 5A.

FIG. 6 is a cross-sectional view of a horizontal gradient coatingdichroic mirror for the off-axis design.

FIG. 7 is a cross-sectional view of a bevel gradient coating dichroicmirror for the off-axis design according to an embodiment of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 5A is a top view of the off-axis design of the dichroic mirror.FIG. 5B is a cross-sectional view of the dichroic mirror viewed alongthe direction of C of FIG. 5A. FIG. 5C is a cross-sectional viewillustrating the light spot taken along the line D-D line of FIG. 5A.Referring to FIG. 5B, the light 502 is not perpendicularly incident ontothe reflective surface 506 of the beam splitter mirror 504, but isincident onto the reflective surface 506 at an angle with respect to thenormal of the reflective surface 506. Referring to FIG. 5C, the lightspot 512 of the light 502 on the reflective surface 506 has a bevelellipse shape. Further, this off-axis design cannot provide a light spot512 with good color uniformity.

For a better color uniformity, a dielectric or metal film can be coatedon the dichroic mirror 504 to change the characteristics of the lightbeam propagation due to the interference effect. However, the coateddichroic mirror 504 can not be a horizontal gradient coating dichroicmirror but must be a bevel gradient coating dichroic mirror for theoff-axis design.

FIG. 6 is a cross-sectional view of a horizontal gradient coatingdichroic mirror for the off-axis design. Referring to FIG. 6, thecoating film on the reflective surface of the dichroic mirror has avariation in the thickness gradient in the direction of arrow E. For thehorizontal gradient coating dichroic mirror, the arrow E is in thehorizontal direction and the incident light with the same incident angleis in the direction of the lines 604. Hence, the direction of theincident light does not depend on the direction of arrow E (thedirection of the variation in the thickness gradient). Because theincident light is off-axis, the primary color distribution of the lightspot is not uniform in the off-axis design.

FIG. 7 is a cross-sectional view of a bevel gradient coating dichroicmirror for the off-axis design according to an embodiment of theinvention. Referring to FIG. 7, the coating film on the reflectivesurface 702 of the dichroic mirror has a thickness gradient orcharacteristic in the direction of arrow F. The arrow F is notnecessarily in the horizontal direction but is depende on the directionof the incident light, for example, the direction of the lines 704,wherein the line 704 is a line indicating the incident light that hasthe same incident angle. By adjusting the direction of the thicknessgradient or characteristic of the coating film and the distribution ofthe thickness or characteristic of the coating film in the direction ofarrow F, the primary color distribution of the light spot can beuniform.

In a preferred embodiment of the present invention, the line 704 may bea curve.

In a preferred embodiment of the present invention, the bevel gradientdichroic film includes a dielectric material or metal.

In a preferred embodiment of the present invention, the bevel gradientdichroic film has a gradient changing film characteristic including adielectric characteristic or a thickness of the film.

In a preferred embodiment of the present invention, the lightcharacteristic of the light spot includes an energy distribution, areflective index, or a light separation ratio for different colorlights.

The present invention provides a liquid crystal on silicon (LCOS)display device. The LCOS display device includes, but not limited to, anoff-axis LCOS display device as shown in FIG. 4.

Referring to FIG. 4, the LCOS display device includes a light source 402for emitting a white light, a color separation mirror 404 for separatingthe white light to three primary color lights 406, 408, and 410, apolarizer 412 for polarizing the three primary color lights 406, 408,and 410, a liquid crystal on silicon (LCOS) panel 414 for partiallypolarizing the three primary color lights 406, 408, and 410 according tothe video component of an input video signal, an analyzer 416, and acolor recombination mirror 418. The analyzer 416 and the colorrecombination mirror 418 combine the partially polarized three primarycolor lights to obtain an output video signal. Then the output videosignal is projected onto the display. The bevel gradient dichroic filmof the present invention can be formed on at least one of the colorseparation mirror 404 and the color recombination mirror 418.

The present invention also provides a method for testing a bevelgradient dichroic film. The method including the steps of providing anincident light having a plurality of incident angles to the bevelgradient dichroic film; and testing a light characteristic of a dichroiclight beam separated from the incident light at each of the incidentangles to determine whether the light characteristic is uniform. In anembodiment of the invention, the method can be an incoming qualitycontrol (IQC) method.

In a preferred embodiment of the present invention, the lightcharacteristic of the dichroic light beam includes an energydistribution, a reflective index, or a light separation ratio fordifferent color lights.

Accordingly, in the bevel gradient dichroic film and the LCOS displaydevice of the invention, the changing thickness gradient andcharacteristics of the dichroic film on the color separation mirror orcolor recombination mirror is dependent on the incident angle of theincident light. Therefore, by adjusting the direction of the thicknessgradient or characteristic of the coating film and the distribution ofthe thickness or the characteristic of the coating film, thedistribution uniformity, brightness, and contrast of the primary colorlight beams can be effectively improved.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

1. A bevel gradient dichroic film, for an off-axis liquid crystal onsilicon (LCOS) display device, comprising: a dichroic film, saiddichroic film having a film characteristic, said film characteristic ofsaid dichroic film comprising a gradient direction; wherein saidgradient direction is dependent on an incident angle of an incidentlight so that a light spot of said incident light on said dichroic filmhas a light characteristic being uniformly distributed.
 2. The bevelgradient dichroic film of claim 1, wherein said film characteristicincludes a thickness of said dichroic film.
 3. The bevel gradientdichroic film of claim 1, wherein said film characteristic includes adielectric characteristic.
 4. The bevel gradient dichroic film of claim1, wherein a material of said dichroic film comprises a dielectricmaterial.
 5. The bevel gradient dichroic film of claim 1, wherein amaterial of said dichroic film comprises a metal.
 6. The bevel gradientdichroic film of claim 1, wherein said light characteristic of saidlight spot includes an energy distribution.
 7. The bevel gradientdichroic film of claim 1, wherein said light characteristic of saidlight spot includes a reflective index of the light.
 8. The bevelgradient dichroic film of claim 1, wherein said light characteristic ofsaid light spot includes a light separation ratio for a color light. 9.The bevel gradient dichroic film of claim 1, wherein said gradientdichroic film provides a uniform distribution of said lightcharacteristic for said incident light with different incident angles.10. A liquid crystal on silicon (LCOS) display device, comprising: alight source, for emitting a white light; a color separation mirror, forseparating said white light into three primary color lights; apolarizer, for polarizing said three primary color lights; a liquidcrystal, on the silicon panel for partially polarizing said threeprimary color lights according to a video component of an input videosignal; an analyzer; and a color recombination mirror, wherein saidanalyzer and said color recombination mirror combining said partiallypolarized three primary color lights to obtain an output video signal;wherein a bevel gradient dichroic film is formed on at least one of thecolor separation mirror and the color recombination mirror, saidgradient dichroic film comprises: a dichroic film, said dichroic filmhaving a film characteristic, said film characteristic of said dichroicfilm comprising a gradient direction; wherein said gradient direction isdependent on an incident angle of an incident light so that a light spotof said incident light on said dichroic film has a light characteristicbeing uniformly distributed.
 11. The LCOS display device of claim 10,wherein said film characteristic includes a thickness of said dichroicfilm.
 12. The LCOS display device of claim 10, wherein said filmcharacteristic includes a dielectric characteristic.
 13. The LCOSdisplay device of claim 10, wherein a material of said dichroic filmcomprises a dielectric material.
 14. The LCOS display device of claim10, wherein a material of said dichroic film comprises a metal.
 15. TheLCOS display device of claim 10, wherein said light characteristic ofsaid light spot includes an energy distribution.
 16. The LCOS displaydevice of claim 10, wherein said light characteristic of said light spotincludes a reflective index of the light.
 17. The LCOS display device ofclaim 10, wherein said light characteristic of said light spot includesa light separation ratio for a color light.
 18. The LCOS display deviceof claim 10, wherein said gradient dichroic film provides a uniformdistribution of said light characteristic for said incident light withdifferent incident angles.
 19. A method for testing a bevel gradientdichroic film, comprising: providing an incident light having aplurality of incident angles with respect to said bevel gradientdichroic film; and testing a light characteristic of a dichroic lightbeam separated from said incident light at each said incident angles todetermine whether said light characteristic has an uniform distribution.20. The method of claim 19, wherein said light characteristic of saiddichroic light beam includes an energy distribution.
 21. The method ofclaim 19, wherein said light characteristic of said dichroic light beamincludes a reflective index of a color light.
 22. The method of claim19, wherein said light characteristic of said dichroic light beamincludes a light separation ratio for a color light.